1. Field of the Invention
The technical field of the present invention relates to a semiconductor device and a manufacturing method of the semiconductor device. Here, semiconductor devices refer to general elements and devices that function by utilizing semiconductor characteristics.
2. Description of the Related Art
A technique in which a semiconductor device such as a transistor is manufactured using an oxide semiconductor as a semiconductor material and the semiconductor device is applied to a semiconductor integrated circuit and an electronic device has attracted attention. For example, Patent Document 1 and Patent Document 2 disclose a technique in which a transistor is manufactured using zinc oxide or an In—Ga—Zn—O-based oxide semiconductor as a semiconductor material and such a transistor is used as a switching element or the like of an image display device.
A transistor in which a channel formation region (also referred to as a channel region) is provided in an oxide semiconductor can have higher mobility than a transistor in which amorphous silicon is used. Further, an oxide semiconductor film can be formed by a sputtering method or the like at a relatively low temperature. Its manufacturing process is easier than that of a transistor manufactured using polycrystalline silicon. For example, Patent Document 3 discloses a thin film transistor in which a zinc oxide thin film formed by a sputtering method in which a pair of targets provided to face each other is used for a channel formation region.